Generally speaking, there are two main types of processes by which detergent powders can be prepared. The first type of process involves spray-drying an aqueous detergent slurry in a spray-drying tower. This process may include the additional step of spraying a surfactant onto a spray-dried base powder. In the second type of process the various solid components are mechanically mixed and optionally agglomerated with liquids, eg nonionic surfactants. The latter kind of process is suited to the production of powders having a relatively high bulk density. However for spray-dried powders postdosed ingredients may be added so that the final bulk density of the product is raised.
Spray-drying is only suited to production of low-to-medium bulk density products because the chemical composition of the slurry used in the spray drying process markedly affects the bulk density of the granular product. This bulk density can only be significantly increased by increasing the content of relatively dense sodium sulphate and/or sodium carbonate. However, sodium sulphate does not contribute to detergency, so that the overall performance of the powder in the wash is thereby reduced.
In some cases, the production of products by mechanical mixing has been described, using a solid starting material which itself has been produced by spray-drying. Obviously, the resultant product will then also contain sodium sulphate.
For a given target bulk density, often the ranges of amounts of surfactants, builders and other ingredients in the detergent granules are limited by the conditions of the particular process in question. This is especially (but not exclusively), the case for producing detergent products having bulk densities spanning the interface between medium and high bulk densities. Further restrictions on formulation flexibility then arise if one tries to minimise the content of non-functional ingredients such as sodium sulphate in the detergent compositions. Obviously such problems are undesirable in the formulation of detergent products.
It is already known to post-dose relatively low amounts of adjuncts of minor ingredients in the form of mechanically mixed granules or spray-dried granules, to a spray-dried detergent powder in order to produce a finished granular detergent composition. For example enzymes, antifoams, or other minor ingredients may be added to spray-dried detergent powders in the form of prills, marumes or granules.
Conventionally, the bulk of the prill, marume or granule is typically formed from ingredients which have no function in the detergent product but which simply act as a filler, for example, sodium sulphate.
In some cases the addition of post-dosed additives in detergent products can lead to a deterioration in the properties of the powders. In particular the dispensing properties and physical properties such as the dynamic flow rate (DFR) may suffer.
It can thus be appreciated that control of the bulk density of a product, whilst retaining formulation flexibility and product characteristics (such as the product's flow or dispensing properties) is a problem; replacing high bulk density components with lower bulk density ones may lead to a worsening of such properties or lower bulk destiny products may not exhibit the same physical properties as their higher bulk density counterparts.
The flow properties of particulate compositions can be measured, for example, by the dynamic flow rate (DFR).
The present invention seeks to address the aforementioned problems by utilising a mixture of granules (in particular granules which have been produced by mechanical mixing) and particles which have been produced by spray-drying. The present invention seeks to provide detergent products having a high degree of formulation flexibility but which retain the desired bulk density range and physical properties eg dispensing properties and dynamic flow rate of the products.
Furthermore the products are especially energy efficient to produce when the granulate is produced by a mechanically mixed method.